In the semiconductor wafer manufacturing environment, in order to protect the wafers from particulate contaminants from ambient sources, the wafers are transported and temporarily stored in hermetically-sealed containers. The hermetically-sealed container for wafers is referred to as a front-opening unified pod (FOUP) and its specifications are standardized internationally. Although the FOUP protects the wafers from chemical contaminants, particulates, and gases from entering inside the container, the FOUP does not protect the wafers from contaminants that may transfer back to the surfaces of the wafers in subsequent process steps as the wafers are removed and returned to the FOUP. For example, contaminants and particles that adhere to the backside of wafer surfaces or to the interior surfaces of the FOUP may fall onto the topside of wafers positioned lower in the FOUP. Also, chemical gases from wafer processing may condense on the topside of wafers or the interior surfaces of the FOUP to cross contaminate other wafers. Such cross-contamination can result in low production yields or loss of the wafers due to defects during the manufacturing process. The problem becomes more acute as the technology node advances where more process steps are involved and the pitch shrinks.